In communication networks, in order to increase the reachable throughput of communication, MIMO (Multiple Input, Multiple Output) has been proposed widely. MIMO involves the use of multiple antennas at both the transmitter and receiver to improve communication performance. It indeed offers significant increases in data throughput without additional bandwidth or transmit power by higher spectral efficiency (more bits per second per hertz of bandwidth) and link reliability.
Multi User MIMO (MU-MIMO) is an advanced MIMO, allowing a station to communicate with multiple users in the same band simultaneously. In an exemplary embodiment of the invention, a mobile communication network comprises a primary station (base station, or NodeB or eNodeB) which can communicate simultaneously with a plurality of secondary stations (mobile stations, or User Equipment, or UE) with MIMO streams, by using a plurality of primary station antennas and a plurality of secondary station antennas. In order to form the stream, the secondary stations provide the primary station with information related to the state of the channel by transmitting CSI (channel state information) feedback to the primary station. Such CSI indicates an optimal or at least a preferred precoding vector to be used in order to maximise the reachable data rate of the corresponding spatially separable data stream transmitted by the primary station. This precoding vector can be a set of complex values to be applied to each antenna port of the primary station during transmission to direct the data stream towards the secondary station antennas.
However, in the context of MU-MIMO, the signalled precoding vector when used may result in a beam which interferes with another secondary station communicating at the same time with the primary station. Moreover, the secondary station is not able to evaluate where interfering stations are located and whether the use of a precoding vector can cause interference.
Moreover, with particular modes of transmissions, like a MIMO mode based on Singular Value Decomposition (SVD), the post processing carried out by the secondary station and the pre processing carried out by the primary station need to be matched, for example to achieve the diagonalisation of the transmission matrix. However, the flexibility of the whole system is affected if the transmission mode, or details of the transmission mode, need to be reinitialised at every event, like the displacement of a secondary station, or the arrival of an interference source in the network. Such a reinitialization would require a huge amount of signalling to reconfigure the transmission system.